Salmonella Type III Secretion-Associated Protein InvE Controls Translocation of Effector Proteins into Host Cells

Salmonella enterica encodes a type III secretion system (TTSS) within a pathogenicity island located at centisome 63 (SPI-1), which is essential for its pathogenicity. This system mediates the transfer of a battery of bacterial proteins into the host cell with the capacity to modulate cellular functions. The transfer process is dependent on the function of protein translocases SipB, SipC, and SipD. We report here that Salmonella protein InvE, which is also encoded within SPI-1, is essential for the translocation of bacterial proteins into host cells. An S. enterica serovar Typhimurium mutant carrying a loss-of-function mutation in invE shows reduced secretion of SipB, SipC, and SipD while exhibiting increased secretion of other TTSS effector proteins. We also demonstrate that InvE interacts with a protein complex formed by SipB, SipC, and their cognate chaperone, SicA. We propose that InvE controls protein translocation by regulating the function of the Sip protein translocases.

肠炎沙门氏菌（Salmonella enterica）在位于63号中心分带区（centisome 63）的沙门氏菌致病岛1（Salmonella Pathogenicity Island 1, SPI-1）内编码Ⅲ型分泌系统（type III secretion system, TTSS），该系统是其致病的关键必需因子。该系统可介导大量细菌蛋白转运进入宿主细胞，具备调控宿主细胞生理功能的能力，且此转运过程依赖于蛋白转位酶SipB、SipC及SipD的功能。本研究证实，同样由SPI-1编码的肠炎沙门氏菌InvE蛋白，对于细菌蛋白向宿主细胞的转运过程不可或缺。携带invE功能缺失突变的鼠伤寒血清型肠炎沙门氏菌（S. enterica serovar Typhimurium）突变株，其SipB、SipC与SipD的分泌量显著下调，同时其他Ⅲ型分泌系统效应蛋白的分泌水平则出现上调。本研究还证实，InvE可与由SipB、SipC及其同源分子伴侣SicA形成的蛋白复合物发生相互作用。据此，本研究提出InvE可通过调控Sip家族蛋白转位酶的功能，实现对细菌蛋白转运过程的管控。